An aspect of the invention is directed to a composition for increasing the viscosity of an aqueous fluid.
Another aspect of the invention is directed to a method for increasing the viscosity of an aqueous fluid.
Another aspect of the invention is directed to producing hydrocarbons from a subterranean hydrocarbon formation.
The use of water soluble polymers and surfactants to increase the viscosity of water is of importance in many applications ranging from improved oil recovery, metal working fluid lubrication, and gellants in the food industry. In a polymer flood, for improved crude oil recovery water-soluble polymers like Xanthan gum and polyacrylic acid derivatives are used to obtain optimum mobility ratios. These polymers in combination with surfactants are known to increase the viscosity of produced brine. The main drawback with the use of surfactants is that they are expensive chemicals and particularly in oil recovery operations tend to deplete in the reservoir due to their adsorption on mineral surfaces. Hence, there is a continuing need for improved compositions for enhanced aqueous viscosification.
It is well known that a significant percentage of oil remains in a subterranean formation after the costs of primary production rise to such an extent that further oil recovery is cost ineffective. Typically, only one-fifth to one-third of the original oil in place is recovered during primary production. At this point, a number of enhanced oil recovery (EOR) procedures can be used to further recover the oil in a cost-effective manner. These procedures are based on re-pressuring or maintaining oil pressure and/or mobility.
For example, waterflooding of a reservoir is a typical method used in the industry to increase the amount of oil recovered from a subterranean formation. Waterflooding involves simply injecting water into a reservoir, typically through an injection well. The water serves to displace the oil in the reservoir to a production well. However, when waterflooding is applied to displace very viscous heavy oil from a formation, the process is very inefficient because the oil mobility is much less than the water mobility. The water quickly channels through the formation to the producing well, bypassing most of the oil and leaving it unrecovered. Consequently, there is a need to either make the water more viscous, or use another drive fluid that will not channel through the oil.
For moderately viscous oils, i.e., those having viscosities of approximately 20-100 centipoise (cP), water-soluble polymers such as polyacrylamides or xanthan gum have been used to increase the viscosity of the water injected to displace oil from the formation. For example, polyacrylamide was added to water used to waterflood a 24 cP oil in the Sleepy Hollow Field, Nebr. Polyacrylamide was also used to viscosify water used to flood a 40 cP oil in the Chateaurenard Field, France. With this process, the polymer is dissolved in the water, increasing its viscosity. While water-soluble polymers can be used to achieve a favorable mobility waterflood for low to moderately viscous oils, usually they cannot economically be applied to achieving a favorable mobility displacement of more viscous oils, i.e., those having viscosities of approximately 100 cP or higher. These oils are so viscous that the amount of polymer needed to achieve a favorable mobility ratio would usually be uneconomic. Further, as known to those skilled in the art, polymer dissolved in water often is desorbed from the drive water onto surfaces of the formation rock, entrapping it and rendering it ineffective for viscosifying the water. What is needed in the art is a composition capable of overcoming the shortfalls of the prior art.